Wide band active circuit three-port circulator for ultra-high frequencies and microwaves

ABSTRACT

An active circuit one octave circulator made of three identical arms interconnected at the three-ports, each arm consisting of a gyrator comprising voltage and current single stage transistorized amplifiers, the impedance at each port being matched with the standard impedance of microwave circuits, and capacitive interconnecting means are provided at each end of the arms and between the two amplifiers. The circulators are designed as microwave integrated circuits.

United States Patent [191 Ropars et al.

[ Jan. 14, 1975 [22] Filed: Jan. 2, 1974 [21] Appl. No.: 429,741

[30] Foreign Application Priority Data Jan. 2, 1973 France 73.0013

[52] U.S. Cl. 333/80 R, 333/1.l, 333/80 T [51] Int. Cl. H03h 7/44 [58]Field of Search 333/l.1, 80 R, 80 T [56] References Cited UNITED STATESPATENTS 3,513.40] 5/1970 Tokunaga 333/l.l X

3,582,803 6/1971 Greenaway et al 333/l.l X 3,700,832 10/1972 Beurrier333/l.l UX 3,716,729 2/l973 Rollett 333/l.l X

Primary ExaminerPaul L. Gensler Attorney, Agent, or Firm-Kemon, Palmer &Estabrook [57} ABSTRACT An active circuit one octave circulator made ofthree identical arms interconnected at the three-ports, each armconsisting of a gyrator comprising voltage and current single stagetransistorized amplifiers, the impedance at each port being matched withthe standard impedance of microwave circuits, and capacitiveinterconnecting means are provided at each end of the arms and betweenthe two amplifiers. The circulators are designed as microwave integratedcircuits.

4 Claims, 12 Drawing Figures PATENTEUJANMISYS SHEET 10F 5 fig.2

PATENTEDJAN 1 4|975 SHEET 3 OF 5 as M fig. 7a

dB A

= fig. 7b

WIDE BAND ACTIVE CIRCUIT THREE-PORT CIRCULATOR FOR ULTRA-HIGHFREQUENCIES AND MICROWAVES BACKGROUND OF THE INVENTION This inventionrelates to a wideband circulator for use in the frequency range from 100megahertz to several gigahertz. The word circulator often relates to anapparatus for microwave operations. It is here used in the followingmeaning. In an n port circulator, with the said ports connected to theirmatched impedance and numbered successively from 1 to n, the applicationof a signal to any port ranked k results in a response only at the port(k 1), when k is lower than n, and at the port 1 when k n.

FIG. 1 illustrates a three-port circulator in which, by way of example,the forward direction of propagation 1 2 3 is counter-clockwise.Circulators are generally based on the microwave properties offerrimagnetic materials. The present invention relates to a circulatorwhich utilises active four-terminal networks which are better adapted tooperation in the lower part of the microwave range, i.e., between 0.1GHZ and several GI-Iz. In an article published with the Applicantsconsent in No. 1 of the magazine Cables et Transmission, 1957, pages 66to 73, under the title Gyrateurs et systmesja. sens unique, MariaPrudhon gives the general relation between the impedances of a nonactiveand non-dissipative fourterminal network, and then shows that in theparticular case of a non-active and non-dissipative linear four-terminalnetwork, called a gyrator, this relation becomes Z =-Z S, S being a realimpedance. The gyrator is described as ideal when the input and outputcircuits impedances are zero and the equations of the voltages as afunction of the currents are reduced to U -SI and U: S1,. The authorthereafter shows that a four-terminal network comprising only idealgyrators and passive elements can have different attenuations in the twotransmission directions provided that the elements other than thegyrators are not all pure reactances, i.e., some of them have aresistive impedance.

PRIOR ART The Applicants filed in 1958, under Pat. No. 1,196,139, aFrench patent application entitled Appareil electrique non reciproque,"in which there is described a fourterminal network which can be used asan isolator in the frequency band from 2.5 to 5 megahertz, the saidapparatus having an isolation higher than 40 decibels and an insertionloss between 9 and l5 decibels, depending upon the frequency.Thereafter, the use of active circuits as gyrators has been describedseveral times in the literature, as well as the interconnection of anumber of gyrators to build up a circulator. D. Rombold describes, inthe March 1971 issue of the Nachrichtenteehnische Zeitschrift pages 121to 176, a circulator having six transistors and three Zener diodes,which has, however, the following limitations:

the highest frequency of the bandwidth remains limited to 30 MHz;

the maximum input power at the ports tolerated without reduction ofbandwidth is in the tenth of milliwatt range;

stray oscillations tend to build up in the circuit owing to the highgain of the voltage amplifiers and makes it impossible to operate thedevice in microwave the band;

two stabilised supply sources are necessary;

the balancing for obtaining the best performances and a zerounidirectional voltage at the ports at zero input signal is critical.

BRIEF DISCLOSURE OF THE INVENTION The object of the present invention isto provide a circulator which can be used above MHz and which is capableof transmitting a power of the order of a milliwatt with a very lowinsertion loss and an isolation of at least 20 decibels within aone-octave band width.

The three-port circulator is obtained by interconnecting three gyratorsmade of identical active circuits, each of which consists oftransistorized voltage and current amplifiers, said gyrators beingdesigned as microwave integrated circuits on a single substrate, inwhich each comprises an input connecting a capacitor, matched with theimpedance of one of the ports of the circulator, capacitive meansconnecting said voltage and said current amplifiers and capacitiveconnecting means between the input of said voltage amplifier and theoutput of the current amplifier of the preceding gyrator.

The advantages of the circulators according to the invention are asfollows:

Since their dimensions are smaller than those of ferrite circulatorsoperating in the same frequency band, their use with microwaveintegrated circuit is easier and provides reduction in the bulkiness ofthe design. For example, a circulator having a bandwidth from 0.55 to lGI-Iz can be designed with dimensions, in mm, of 35 X 35 X 14 or 28 X 39X 14. If miniature coaxial connectors are used, the aforesaid dimensionsare re duced to 35 X 35 X 6 millimeters and the circulator weighs a fewgrammes. A ferrite circulator marketed by the Assignee under thereference number R 2947 B, having the same bandwidth, and comparableisolation and insertion loss values, weighs 1.3 Kg and occupies thevolume of a cylinder of a diameter of millimeters and a height of 40millimeters, which makes it impossible to introduce it in an integratedmicrowave design.

With equal overall dimensions, the bandwidth of active-circuitcirculators is very much higher than that of ferrite circulators. As anexample, reference is made to types F 58100 A and F 58101 A circulatorsmarketed by the Assignee. The overall dimensions are those of a cylinderof a diameter of 50 millimeters and a height of 20 millimeters. Thefirst covers the bandwidth between 70 and 360 MHZ and the second thebandwidth between 200 and 500 MHz. In order to scan each of these twobands with ferrite circulators, it is necessary to use four differentdevices, each having a volume equivalent to that of the uniqueactive-circuit circulator.

The circulator according to the invention requires a single supply, ofwhich one output is earthed, and consequently there is no problem ofbalancing the voltages.

The circulator according to the invention may be operated in the veryhigh-frequency and microwave ranges. As higher cut-off frequencytransistors become commercially available, it will be possible tointroduce them into the circulator according to the invention withoutmodifying the circuit design and the maximum operating frequency of thecirculator will be raised accordingly.

DETAILED DESCRIPTION OF THE INVENTION Further features and advantages ofthe invention will become apparent in the course of the descriptionillustrated by FIGS. 1 to 10, which are given purely by way ofillustration and have no limiting character, and in which:

FIG. 1 shows a three-part circulator,

FIG. 2 is the block diagram of the circulator according to theinvention,

FIG. 3 is the electric circuit diagram of one of the gyrator arms of thecirculator,

FIG. 4 illustrates, the design of the circulator,

FIG. 5 illustrates the input standing wave ratio of a circulator of afirst type, as seen from the outside,

FIG. 6 illustrates a variant of the matching circuit of the ports of thecirculator,

FIG. 7a illustrates the insertion loss of a circulator of the first typeand FIG. 7b that of a circulator of the second type,

FIG. 8a illustrates the isolation of a circulator of the first type andFIG. 8b that of a circulator of the second type,

FIG. 9 illustrates the figure of merit of a circulator of the firsttype, and

FIG. 10 illustrates an example of the variation of the insertion lossand of the isolation of a circulator as a function of the amplitude ofthe input signal.

In FIG. 2, in which the ports of the circulator are denoted by l, 2 and3, voltage amplifiers 30 are connected to current amplifiers 31 bycapacitors 32; capacitors 33 connect the output of the amplifiers 31 tothe following amplifier 30. The ports of the circulator are connected tothe input of the voltage amplifiers by means of capacitors 34. Thesupply of the amplifiers is not shown.

In FIG. 3, which partially shows the electric circuit diagram of thecirculator, the interrupted-line contour 4 surrounds one of the threeidentical gyrators. Each of them comprises two transistors, i.e., thetransistor 5 connected as a voltage amplifier corresponding to thereference 30 in FIG. 2, and the transistor 6 connected as a currentamplifier corresponding to the reference 31 in FIG. 2. The transistor 5is connected through a capacitor 7 to the port which precedes it, andwhich is denoted by way of example by the numeral 2 in FIG. 3, andthrough a capacitor 8 to the current amplifier which precedes it.Resistors 9 and 10 form a bridge between earth and the general supplyvoltage available at the end of a resistor 21 connected to a capacitor22. The base of the transistor 5 is connected to the intermediate pointof this bridge. In addition, it is connected by means of a capacitor 7in series with a low-value inductor 14 to the port 2 and by means of aresistor 12 adjusted to an optimum value in the neighbourhood of 50 ohmsin accordance with the operating frequency band in series with acapacitor 8 to the emitter of the output transistor of the precedinggyrator. A 50-ohm resistor 13 connects the emitter of the saidtransistor to the emitter of the transistor 5. A SO-ohm resistor denotedby ll connects the emitter of the transistor 5 to earth. The capacitors7 and 8 have the same capacitance value, for example 4,700 picofarads.

A capacitor 15 connects buffer resistor 16 of the transistor 5 to thebase of the transistor 6. The base of the latter transistor is inaddition connected to the resistors 17 and 18. A resistor 19 of lowvalue is connected between the collector of the transistor 6 and thatend of the resistor 21 which is connected to the decoupling capacitor22. A high frequency capacitor 23 of low value is connected in parallelwith the capacitor 22. A resistor 20 of a value of ohms provided betweenthe emitter of the transistor 6 and earth constitutes the output of thecurrent amplifier.

FIG. 4 illustrates the design of a circulator according to the inventionaccording to microwave integrated circuit technology. The standardized50-ohm microwave outputs 41, 42, 43 serving as ports are fixed to thecasing 45. The amplifiers 30 of FIG. 2 are formed by the transistors 40,while the current amplifiers 3l consist of the transistors 44.Transistors 35 821E marketed by the company Hewlett-Packard, transistorsMS 175 marketed by Texas Instruments, transistors BS-Tl4 manufacturedand marketed by the Assignee have been successfully used in such design.The main technical data for this transistor, are as follows: maximumoperating frequency 6 to 7 GHz, cut-off frequency 4.5 GHz, noise factorat l GHz 2 dB, maximum power 100 milliwatts. The supply means for thecirculator, which is separated from the closed metal casing 45, isconnected by a coaxial line 46 having its sheathing connected to theearth of the casing.

The circulator operates as follows: the transistor 5 of FIG. 3 islocated on the diagonal of a Wheatstone bridge consisting of theresistors 11, 12, 13 and the purely ohmic impedance of the load as seenthrough the port 2, which is balanced if the load is appropriate,because the capacitances 7 and 8 balance one another. Any signal comingfrom the resistor 20 situated on one of the diagonals of the bridgegives a zero resultant in the other diagonal, in which the transistor 5is situated. The signal coming from the port 1 therefore cannot betransmitted to the port 3. On the other hand, in the arm at which theport 2 is connected, a signal appears which is transmitted through thelatter to the output owing to the fact that its coefficient ofreflection in this direction is zero. It is necessary for this conditionto be satisfied throughout the operating frequency band. This involvesforming the ports by means of coaxial standard 50-ohm outputs to whichare connected coaxial connectors and coaxial cables of the samestandard. As seen from the outside through each port, the circulator isalso matched. This result is obtained in a satisfactory bandwidth bymeans of an inductor made of two turns of wire having a diameter of 1.6mm, coiled on a diameter of 20 mm, which are denoted by 14 in FIG. 3.However, when the frequency band of the circulator reaches the microwaverange, the bias of each transistor 5 is experimentally adjusted in suchmanner that its cut-off frequency is maximum. The matching of each portof the circulator in a large bandwidth is then obtained by means of amore elaborate network of impedances.

FIG. 5 illustrates the standing wave ratio of a first type of circulatoras seen from the outside through any one of its three ports. This figureshows that the frequency band in which this type of circulator can beoperated extends from to 500 megahertz. As an illustration of what hasbeen stated in the foregoing, FIG. 6 shows in the interrupted-linesquare a circuit for matching the ports of a second type of circulatordesigned with transistors BST 14 in the frequency band from 300 to 1,000MHZ. This circuit comprises a series inductor 62 whose characteristicsare substantially the same as those of the inductance 14, a capacitor 63(12 picofarads, for example), in series with a resistor 64, (for exampleof 220 ohms). The latter two elements are connected between earth andthe common point of the This bandwidth can be modified by changing theoperating frequency of the Wheatstone bridge at the input of eachgyrator. This is obtained in practice by slightly changing the bias ofthe transistors 5. By way of example, the following results are obtainedwith the same circulator:

inductance 62 and the capacitor 7.

FIG. 7a illustrates the insertion loss, in decibels, of a circulator ofthe first type with respect to frequency. As this curve shows, atfrequencies below 350 MHZ the circulator amplifies any wave enteringthrough any one of its ports and leaving by the following one in thedirect circulating direction of the circulator, and at frequencies above350 MHZ it attenuates a wave propagating in the same circulatingdirection.

FIG. 7b illustrates the insertion loss of a circulator of the secondtype.

FIG. 8a illustrates the isolation in decibels of a circulator of thefirst type.

FIG. Sbillustrates the isolation of a circulator of the second type.

FIG. 9, which is derived from FIGS. 7a and 8a, is a curve illustratingthe figure of merit of a circulator of the first type as a function offrequency; it shows the ratio of the power of the forward wave to thatof the backward wave in decibels.

In PK). 10, the curve denoted by 101 shows the insertion loss and thecurve denoted by I02 shows the isolation of a circulator of the firsttype. measured at 200 MHZ, as a function of the amplitude of the voltageof the input ultra-high-frequency signal.

Measurements of the bandwidth of the circulator of the first type as afunction of the input power have given the following results with aninsertion loss of 1 dB and an isolation of 16 dB:

with an input power of0.5 mW the band spans I50 500 MHz do lmW do 200500 MHz do 2 mW do 220 350 MHz do 5 mW do Noise measurements were madewith rdriffeL nt designs of the circulator. As a typical result in acirculator, with transistors 35821 E the value of the noise factor is8.5 dB at 60 MHZ and II dB at 250 MHZ.

We claim:

I. A wide band active circuit circulator made of three identicalgyrators serially interconnected comprising each a current amplifier anda voltage amplifier serially connected and three ports respectively atthe interconnections between two gyrators which comprises firstcapacitive coupling means between each port and the input of theconnected gyrator, second capacitive coupling means between each portand the output of the connected gyrator, third capacitive coupling meansbe tween said current and voltage amplifiers of the same gyrator, and asingle supply means for said amplifiers one output of which is earthed.

2. A wide band active circuit circulator according to claim 1 in whichsaid first and second capacitive coupling means contain capacitors ofthe same value.

3. A wide band active circuit circulator according to claim 1 in whichsaid first capacitive coupling means is serially connected with animpedance matching section.

4. A wide band active circuit circulator according to claim 3 in whichsaid impedance matching section consists of a series capacitorinductorcircuit.

several MHz around 220 MHz.

1. A wide band active circuit circulator made of three identicalgyrators serially interconnected comprising each a current amplifier anda voltage amplifier serially connected and three ports respectively atthe interconnections between two gyrators which comprises firstcapacitive coupling means between each port and the input of theconnected gyrator, second capacitive coupling means between each portand the output of the connected gyrator, third capacitive coupling meansbetween said current and voltage amplifiers of the same gyrator, and asingle supply means for said amplifiers one output of which is earthed.2. A wide band active circuit circulator according to claim 1 in whichsaid first and second capacitive coupling means contain capacitors ofthe same value.
 3. A wide band active circuit circulator according toclaim 1 in which said first capacitive coupling means is seriallyconnected with an impedance matching section.
 4. A wide band activecircuit circulator according to claim 3 in which said impedance matchingsection consists of a series capacitorinductor circuit.